With the advent of semiconductor devices having increasingly large component densities, the removal of heat generated by the devices has become an increasingly challenging technical issue. Extrapolating the ongoing changes in microprocessor organization and device miniaturization, one can project future power dissipation requirements of 100 W from a 1 cm by 1 cm core CPU surface area within the easily foreseeable future.
Typical processor boards sometimes include multiple CPU modules, application-specific integrated circuits (ICs), and one or more types of memory such as static random access memory (SRAM), as well as dcxe2x80x94dc converters, all of which have different and extreme power dissipation requirements. Adding to the complexity, the variety of chip types on typical processor boards provides for chip surfaces at a variety of heights off the board""s surface.
Highly available computer systems, to prolong a customer""s investment, are designed to both be maintained for long periods and to be easily maintained over time. This makes it preferable that a computer system is well cooled across all of its components on each board, and that the computer can quickly and readily accept upgrades for boards as they become available. The evolution of the design may include one or more of the following: new or additional components, changes in existing component locations, and increased power dissipation due to technology changes.
In the past, the low power dissipation of the processors accommodated the use of low cost, air-cooled heat sinks that require minimal re-design effort. However, with higher dissipation requirements come more complex cooling systems that make both the even cooling requirements and the serviceability of a board a more complex issue. In particular, board upgrades will typically have different layouts of chips with different dissipation requirements, thus requiring cooling systems that adapt to the layouts and requirements of the new board while providing high levels of heat dissipation.
Spray cooling technologies can offer high dissipation levels that meet extreme cooling requirements. With reference to FIG. 1, in spray cooling, an inert spray coolant from a reservoir 11 is preferably sprayed by a group of one or more sprayers 13 onto an aligned group of one or more chips 15 mounted on a printed circuit board 17. The coolant preferably evaporates, dissipating heat within the chip. The sprayers and chips, and the board, are mounted within sealed cases 19 fixed within a computer system. The sprayed coolant is typically gathered and cooled within a condenser 21, and then routed back to the reservoir by a pump 23.
The cases are evacuated systems with sprayers fixed at locations conforming to the layout of the respective chips to be cooled, and targeted toward those chips. Thus, for a liquid cooled board, board-upgrading becomes a complex issue that would typically be dealt with by replacing the sprayer set with a new set configured for the new board.
It is known that the thermal performance achieved from spray cooling is dependant upon the spraying distance between the sprayer and the hot surface of the chip. A greater distance allows for more of the cooling fluid to evaporate prior to reaching the chip. Furthermore, drag reduces the speed of the droplets, allowing even more cooling fluid to evaporate prior to reaching the chip. The evaporation of cooling fluid prior to reaching the chip reduces the fluid flow rate received by the chip, and thus reduces the thermal performance of the spray cooling system. The reduced speed of the droplets also reduces their momentum, and thus their ability to penetrate vapor barriers, such as can form at near-local-maximum levels of heat flux for a spray-cooling system. As a result, the height of the sprayers off the board is typically set to be the optimal height for cooling the hottest and/or most critical chip on the board.
Upgrading the board is further complicated by this issue of sprayer height off the board (and its chips). Because the hottest chip of a new set of chips would likely have a different height, temperature, and location on its respective board (as opposed to the hottest chip on the original set), the height of the sprayers off the board would typically need to be adjusted accordingly for each board change.
Accordingly, there has existed a need for an easily maintainable spray cooling system that maximizes spray cooling efficiency for a plurality of components on a single printed circuit board, while being adaptable to new board layouts. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.
In various embodiments, the present invention solves some or all of the needs mentioned above, providing a cooling system that can efficiently adapt to cool a variety of component configurations with little or no reconfiguration of hardware.
The invention can include or form a cooling system for cooling one or more hot portions of one or more heat-producing components, such as semiconductor devices, on a board by spraying the components with a cooling fluid during the components"" operation. The hot portions of the heat-producing components cover sections of a target area, while not covering other portions of the target area. The target area can be a substantial portion of a side of a printed circuit board. The cooling system of the invention includes two or more structurally interconnected spray-cooling nozzles configured to eject droplets of cooling fluid targeted throughout the target area.
The invention features a controller to control the nozzles, the controller being configured to use information that delineates the sections of the target area covered by the hot portions of the heat-producing components. At the controller""s direction, a first group of one or more nozzles is energized to be substantially active, while a second group of one or more nozzles is substantially inactive. The first group is targeted such that they can cool the hot portions of the heat-producing components, while the second group is targeted at sections of the target area that are not covered by the hot portions of the heat-producing components (i.e., they are not targeted to cool hot portions of the heat-producing components).
Advantageously, this feature of the invention allows the cooling system to be configurable for a wide variety of component layouts. To change the system""s configuration for a new layout, the cooling system must generally be programmed or otherwise provided with new information delineating the portions of the new layout that need to be cooled. That information can optionally be provided by the new board. Incremental sprayers, and particularly inkjet-type sprayers, are particularly useful for this feature because of their inherent controllability.
The invention further features an enclosure that defines an internal chamber configured to contain the board. An electrical connector within the chamber is configured to electrically connect to the board, enabling the operation of the components. The nozzles are located within the chamber.
In a first variation, the chamber can be readily opened and closed by hand for external access to the chamber. When the chamber is opened, the board can be readily removed and replaced by hand. During operation, the chamber is closed and sealed such that cooling fluid cannot leak out of the chamber. This feature provides for efficient replacement of the board, potentially without shutting down the entire system of which the board is a part, i.e., making it hot-plugable. This feature, in combination with the first feature, typically provides a spray cooling system that allows for boards to be efficiently upgraded without mechanically reconfiguring the system.
In a second variation, the enclosure can be configured for releasably inserting into a bay of an electronic device, the bay having an electrical connector. The enclosure includes a second electrical connector on the exterior of the enclosure, configured to mate with the electrical connector of the bay to place the board in communication with the electronic device via the first electrical connector. This feature provides for efficient replacement of the combined board and cooling system with another, potentially without shutting down the entire system of which the board is a part. The cooling system can then receive a new board, possibly with a different layout, and be used again.
Additionally, the invention advantageously features the controlled operation of the first group of sprayers such that the cooling system adjusts their flow rates to compensate for their distances from each cooled component. This feature provides for efficient and effective cooling of the components on the board, allowing for each component""s height.
Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The detailed description of particular preferred embodiments, as set out below to enable one to build and use an embodiment of the invention, are not intended to limit the enumerated claims, but rather, they are intended to serve as particular examples of the claimed invention.